The invention relates to a cage rotor for an asynchronous machine comprising starting bars for improving its starting behavior. The invention further relates to a method for manufacturing a cage rotor of this type.
A cage rotor is known from JP 1028360 A in which the operating bars made of copper are inserted into grooves of a laminated rotor core such that said bars rest against a radially inwards-directed groove base of the laminated rotor core and a residual cross-section not filled with the operating bars remains in a radially outer area of the grooves. This residual cross-section is filled with molten aluminum in a die casting process. After the melt has hardened starting bars made of aluminum are thus formed which, as a result of the material used, have a higher electrical resistance than the operating bars made of copper.
As a result of the skin and proximity effect the secondary current of an asynchronous machine is displaced during starting of the machine in the direction of the outer groove area. Since the starting bars made of aluminum are arranged in this outer groove area, the asynchronous machine experiences a high resistance during starting which in its turn has a favorable effect on the torque behavior of the machine. As soon as the machine has reached its rated speed the secondary current essentially flows in the better-conducting operating bar made of copper. The efficiency of the asynchronous machine is in its turn influenced in a positive manner by this.
So-called double bar grooves are also widespread in cage rotors with operating and starting bars, in which, as seen radially, an internal groove made from a more conductive material is provided and, as seen radially, an outer groove is provided for a starting bar with lower conductivity. The two grooves are separated from one another by a scatter web.